Top 5 Most Common Koi Pond Problems and Their Solutions

Having a Koi pond can not only increase the visual appeal of a property, but it can also aid in developing a passion for an environment that you are able to maintain for yourself. Koi ponds can certainly encounter a number of issues throughout time, especially considering the amount of time and effort that one puts into maintenance, but this does not mean that such problems cannot be solved and alleviated with a few simple suggestions. The following will outline 5 of the most common problems associated with Koi ponds, as well as ways in which such problems can be solved.

Predation is a serious issue with Koi ponds, especially during the overnight hours. Cats, raccoons, and even larger coyotes have been known to prey on the fish in Koi ponds. If you are finding this to be an issue for you and your fish friends, then consider making the water too deep for large birds or animals to stand in or place netting on the surface of the water to pose as a barrier between the fish and the predator.

Parasitic infestations of your fish can not only be difficult to identify, but they can be nearly impossible to identify as many are too small for them to be seen by the naked eye. If you are experiencing an issue of this nature, then consider a better filtration system such as one that incorporates a UV sterilizer. For more on koi diseases see this article.

If you find that your Koi pond has excessive algal growth which can decrease your ability to see your fish, then there are several ways to manage the algae in your pond. You can choose to either tint the pond water, which will reduce the ability of the algae to gather sunlight, or you can add just a slight amount of salt in the pond, but only if you do not have other plants growing that don’t have some salt tolerance.

Low oxygen levels can certainly be one of the leading causes of the death of Koi fish. Unfortunately, many people do not realize that they are having this issue until it is too late. Adding plants, air stones or a small fountain or waterfall to your pond should create sufficient oxygen and flow to keep your fish alive and happy.

High pH levels and high bacteria levels can all contribute to the death of fish. Koi ponds may have a pH range between 6.8 to 8.2 but 7.0 to 7.5 is really ideal. There will most likely be natural daily swings of pH of a small amount but that is not something to be concerned about as long as they are small. The concern becomes big swings in a short time or generally pH levels that are outside the acceptable range causing koi skin to become vulnerable to bacterial infection. Two main solutions to keeping pH levels in check are regular testing and if need be adjustments via buffers and acids. In short, buffers will increase pH while the addition of acids will reduce pH.

75 Responses to Top 5 Most Common Koi Pond Problems and Their Solutions

We are located in New England and have a large pond fed from natural wet lands. We rely on nature to filter the water. This has worked well for us and the 30 koi who share the pond with the local frogs and fish.

For the first time in the 10 years we’ve had koi, I have noticed an irregular shaped bump on the back of one koi. This was first notice about two months ago, in May. I have not noticed any similar bumps on th other koi. The pond is too large to net tho koi for closer inspection. Can adding salt to the water help heal this fish? Will the salt cause any problems downstream? How can we determine the amount of salt that would be healthy for this environment?

The water from the marsh can be very dark during the warmest days of summer. It occasionally has a film that looks like an oil slick. The fish dont seem to mind but we dont care for it. Would salt clear the water? Can you recommend some non invasive plants or natural additives which would be good for this open environment?

I would be cautious about adding salt as a whole-pond treatment. Though the koi can handle a certain amount of salt exposure for a limited time you risk affecting other plants and animals in the system. Really the best thing to do is to somehow lure your affected fish over (perhaps with koi chow) and net it up and quarantine it. You may have to eventually cull this fish as if won’t be worth losing your whole group for one fish. As for the oil slick I can’t say I know off the top of my head what that is but it clearly has something to do with the increased biological activity of the system associated with increasing temperatures. With respect to plants that would be ideal for your pond I would say water lillies are a great choice as well as Elodea (American water weed). Elodea is great for cover and for producing dissolved oxygen (DO) in the water (which is nice for hot days that can create a low DO scenario). Another cool thing is that even it gets uprooted, say by a rooting koi, it can still grow unattached to the sediment. Hope this helps.

We are located in California and we have a 500 gallon pond with 4 koi fish that are each about 10 inches long and around 6 goldfish that are 1-2 inches long. We have a two foot wide water fall connected to a 3600 gal/hr pump and a large skimmer basket. We built the pond about 2 months ago, but we still have problems with green water/algae. I was wondering if you have any suggestions on how to clear the water. We have 4 large plants and two water lily clusters.

Green water which is essentially single celled algae is often associated with spring and summer as that is when ponds begin to experience increases in sunlight and water temps.- both important elements for algal growth. However, another element that aids in algal growth is nutrients such as nitrates. So right off the bat check your water chemistry and make sure you’re not feeding to excess which can result in higher nitrate levels. There are chemicals out there as you’ve discovered that will help to mitigate for green water and those include a products like AlgaeFix and Accu Clear. To really get at the heart of the problem though your water chemistry comes first and after that the next best approach is an in-line UV light as part of your filtration system. UV is a very effective control for algae and doesn’t involve chemicals that have the potential to complicate things.
Hope this helps.
Good luck

I can’t seem to get an algae infestation cleared up. The pond was just power washed 3 weeks ago. Within a few days algae growth began. Now the pond liner is covered with string algae up to 12 inches long. I have added plants in the waterfall stream and 4 lilies , 2 giant marigold… The pond is in an open area and gets sun all day.

String algae won’t do well unless the conditions are right and that means more than just plenty of sunlight. You most likely have the proper nutrients in your pond to spur the growth of this algae. The usual suspects are phosphate and nitrates. Excessive nitrates are the result of nitrogenous waste from your fish and any uneaten food will yield phosphates. The problem is you can use something like Algae Fix to effectively kill the algae but you will still have to remove it anyway b/c once it dies and begins to decay and that will result in an eventual increase in nitrites and nitrates(http://koi-care.com/understanding-biological-cycle-koi-pond/). So test your water and see where your levels are (http://koi-care.com/ideal-water-conditions-healthy-koi/) and begin to deal with your water chemistry then consider the plant coverage in your pond. Lillies are great for providing cover and essentially keeping your pond cooler and inhibiting as much sunlight penetration. Try for 60-70 percent surface coverage. I know you just planted some additional plants but try to hit that coverage goal. I think once your water chemistry to brought back to the proper levels I would just remove the string algae manually (in the beginning) rather than going right for the Algae Fix.
Good Luck

I live in Central VA and have about 15 koi in a 1000gal pond. Yesterday the fish (all of them) were frolicking around like crazy all day, chasing each other all around. This morning 2 are dead and the rest are very lethargic. I don’t know what’s going on. Could they have stirred up stuff in the bottom of the pond and made the water toxix? I haven’t been able to find anything on the web addressing these symptoms.

yes, this is possible. Toxic gasses can be released from sediments and muck built up over time but it typically occurs if someone walks through it quite a bit or the muck is mechanically dredged. Spring and summer are times when koi will breed so I am thinking that what you had was some mortalities due to breeding competition between males and/or an excess of males on the female(s). A ratio of two males to one female is recommended -anything more may cause problems. A full moon will also help to initiate mating but an approaching storm with its associated low pressure will also spark mating as well -do you remember if had a storm around the time they were chasing each other around?

I live in RI, my pond is about 7000gal. I have two bio filter pumps with waterfalls, two UV lights and I have been using a lot of beneficial bacteria, barley and algae fix. My water is olive green, I cant see the fish, and there is a constant accumulation of a thick olive green sludge that is all over the lining and several inches thick on the bottom. I have vacuumed it out several times, we have done a 2000gal water exchange, and I recently added an aerator. But the olive green sludge just keeps coming. I’m desperate!! Any ideas?

having the UV is great but they may be getting weak (towards the end of their life) or the glass of the light may be obscured in some way by particulates. It sounds like you are taking all the right steps. One thing you may want to try though is koi clay. Its totally natural and you may just find that its the silver bullet to your green water problems. Obviously you will want to keep an eye on your water chemistry too -if that is too high in nutrients its just fueling your algal growth.

I have had a KOI pond for four years when I bought a house. Never had an issue, the pond is in an atrium that gets sunshine but some of the outside elements aren’t able to get in. No issue until about a week ago with green algae. I treated the water and it has cleared up but now I have lost on of my fish and the other two don’t look so good. At a loss to be honest.

t sounds like the green algae is an indication of a larger problem and that problem most likely lies with your water chemistry. You can’t have algae doing well with just sunshine or just nutrients -they need to have both of those elements in the equation to thrive. My guess is that your filtration is not as effective as it used to be and not removing those excess nutrients that are allowing the algae to do well. So two things: first I would look into UV sterilizers to add to your filtration system (its generally a good idea to have that in play especially if your algae is the free floating, green water type) and second I would look into giving your filtration media a boost with a “microbe-lift” or something similar. Make sure you’re not overfeeding either or that something isn’t dead on the bottom (or anything obvious like that).

When the waterfall in our koi pond is turned on there is an awful odor; I want to say methane but I’m not sure about that. Also, the water is very green even though the pond was recently cleaned. Unfortunately, the pond is direct sunlight most of the day. We do have plants in the pond and about 9 koi in a 1200 gallon pond.

The smell from your water sounds like a sulfur smell that is typically associated with well water-is that the source of your pond water? The other thing it could be and this may be a long shot is that the action of the falling water reaching the bottom of your pond (not sure how deep it is where your fall empties) is stirring up anoxic mud which will also have a sulfur/low tide smell.
As far was the green water goes there’s lots of good solutions for that but the best thing would be to see my latest article on dealing with algae. I can tell you though that a big asset in dealing free floating algae like what you have is a UV sterilizer.
Good luck, grant

May pond is always turning green can a put a sun block shade offer the pond to proven turning green. I do have the uv light and filters on the pond. This morning one off may koi’s is swimming on his side what can that be? I am living in South Africa

Brenda,
There are many things you can do to deal with green water. I will direct you to my recent article on this subject but in the meantime yes, you can put a shade over the pond, you can add a dye to the water that will block a lot of light penetration into the water and prevent the free floating algae from receiving light. You can add something called “koi clay” that will help with green water and your koi will love it. You need to check your UV sterilizer -is it dirty? is it big enough for your pond size? is the bulb getting older and less effective? Is your filtration sufficient for your pond size? Remember that as fish grow or as you add fish you add more demands on your filter system so what worked 3 years ago may not be sufficient now.
A koi swimming on its side could be a lot of things -may be an air bladder issue. Its hard to tell at this point. Possibly an internal infection.
-Grant

I have a 10,000 gal. pond.
In it I have 4 – 10lb koi and about 30 various size gold fish.
Last spring when I moved them outside for the summer they were fat and healthy. By mid-summer one of them always stayed in the shallows amongst the water lilies. It almost never came out for feedings. When I brought them in for the winter this one was very shinny and had the appearance of a Sturgeon. Is it possible it could have a tape worm? what could be wrong with it and how do I treat it? I am afraid I might loose this 6 year old Koi
Randy

Randy, well the shiny description is usually a product of carp pox which wouldn’t typically be fatal or cause the sturgeon look (which i am assuming is a thin, gaunt look) So if your fish is losing weight consistently then I would tend to conclude that it is “skinny disease” which is bacterial in origin. Here is an excerpt from my site:

Treatment: Adding extra food to the fish’s diet can usually clear up this disease. However, sometimes this doesn’t help and if the bacterial infection persists, adding erythromycin to the fish’s food normally clears the infection up quickly.

You will want to quarantine this fish no matter what you do as its hard to treat a specific fish when its mixed in with the others and is withdrawn. You may want to do a light salt treatment in quarantine to allow the fish a little osmotic relief while it fights the infection.
-grant

I have plans to renovate my pond this coming summer so I moved the Koi into a large tank. The Koi have become quite aggressive when I come into the room feed them, so much so that the thermometer I put in the tank has been broken. Not a big deal in itself but it appears that one (or more) of the fish may have eaten parts of the thermometer. the parts are big enough that I don’t believe the fish will pass them. Is there something I can\should be doing? The fish appear to be healthy.

Please help, I have large koi in my pond around 18in
Long and weighing around 3-31/2 pounds, I’ve already lost one
and possibly going too lose another.
The fish seems to roll onto its side as if dying , then speeds of up / across
The pond as if full of life?
I’ve tried bacterial medication, and fungal medication,
I must confess I’m no pond expert and wondering if I’m doing something wrong.
My ponds 21ft- 6ft well circulated water and two waterfalls,
2-5ft depth holding 800 imp gallons. Please, please help.
Jim Glasgow Scotland.

Hi Jim,
First things first I would isolate your fish in a quarantine tank to be able to treat better (you may also want to put a heater in the quarantine and raise the temp up slightly). Secondly, one thing that comes to mind in terms of causes is costia so you may want to do a scrape for that,. Second thing that comes to mind is water quality. As this is Spring in Glasgow, you will often experience a bad combination of immune-depressed fish coming out of winter mixed with lower levels of beneficial bacteria in your filter media which results in the water quality going down and allows things like costia and other parasites to thrive. So test your water and of course look for high ammonia and nitrites. Do water changes as necessary and boost your filter media with beneficial bacteria (something like Microbe-Lift PL).
hope this helps, grant

Came home this evening and the pond had a very strong fish smell. One dead KOI the rest seem to be fine. Just bought the place towards the end of last year. Have a local pond company coming this Friday to empty and clean the pond. Called and left a message with them tonight but was hoping you could answer this tonight to see if there is something I should do to save the rest of the KOI.
Thanks

That’s tough to say what happened to your dead koi but the first thing I would do is check water chemistry- most problems stem from water issues. As it is spring you will see immune compromised fish having issues with poor water quality as they come out of winter dormancy.

This is my first koa pond, I started it about two month ago. I came home tonight and one of my fish had died. Imy wondering if I have caused this when I put the Algae Fix in the pond. Would you advise me to take out the other fish until I figure out the problem?

I also had a small 120 gallon water feature with some plants and small koi and goldfish. About 3 weeks in the water was getting rather green even with a fountain and bubbler. I added Algae fix and:
Day 1: Dead goldfish
Day 2: Dead Koi

Green water algae won’t grow without the right conditions like high Ammonia and nitrites so I suspect your water chemistry is out of line. Algaefix might kill the algae but the water chemistry issues still persist. That’s where I would start if I were you.

We are having huge issues with our 125 gallon pond. It is fairly new, about 2 and a half months and we are in south Texas. Over the course of 2 weeks, we have had many problems with our koi and goldfish. We have 6 small medium sized koi and goldfish ..I do regular water changes, about half to 3/4 and have used Prime and Stress Enzyme each time. Over the few weeks algae has become a major issue. I noticed that the koi would hide in their fish home at the bottom of the pond whenever I would do an algaefix treatment. They wouldnt come up to eat at times. We went away for a weekend vacation and had my mom come feed once a day and when we came back the water was almost like a green milk, but 2 days prior we had gotten the water pretty clear, as clear as it could be considering its summer. I did a 3/4 water change, did stress treatment and algae and had 1 koi start swimming sideways, died later. 5 goldfish also died the same way. Little did I know the chlorine was at toxic levels because I didnt put enough Prime in. We did another water change with Prime and the rest of the fish made it through. 3 days later we went on vacation for 5 days, just came back last night. Water did the same thing, green milk appearance, even though my mom was doing algaefix and routine 6 in 1 strip testing. I did a water change last night and treated the water with prime, stress enzyme and algefix. This morning the fish refused to eat.. they were all confined to the bottom of the pond. I checked the water, everything seemed fine except a small increase in chlorine and the water was still murky even after the water change. I did one more change, same treatments, this morning. I also placed a few lava rocks in our pond filter box. Hours later our smallest goldfish died and all of our 6 koi started coming up gasping for air. I shoukd note that We have a fountain and a pond pump that does 200 gallon per hour. Well, I started researching and assumed that this koi behavior was an oxygen problem, so we bought an aerator. An hour after running it, koi were still having issues and a water test showed very high alkalinity. Had one of our oldest koi start swimming sideways and die. 2 have been frequenting the top for the past few hours.

How did our pond go from being normal, no deaths, for weeks and weeks, with the same style water changes to now koi dying and goldfish. What am I doing wrong? We are new to ponding but trying to figure it out.

1) when you do massive water changes you run the risk of major pH swings and that can cause problems.
2) green water appearance is free floating algae which means you have conditions that support algal growth such as high ammonia and nitrites. Suggest a UV filter and/or giving your filter media a boost with Microbe-Lift PL
3) south texas is hot -what kind of water temps are you seeing? Fish that are already suffering from say chlorinated city water and then you stack on top of that low dissolved oxygen and higher water temps it magnifies whatever problems the koi were having.
4) its probably worth a read (http://koi-care.com/getting-rid-of-algae/) my article on algae in koi ponds should help your situation.
5) your high alkalinity may be attributed to multiple things but the big water changes are most likely one of them.
As you are prob. figuring out, most problems usually originate from water chemistry/quality so if you can navigate your way through that you will be able to handle most issues that come up.
-Grant

A client wants a Koi pond and the tempratures vary in India from 12 to 40 degrees Centigrade. The pond is 50m long and 3m wide and 1.2m deep, loosing water. They want a liner with rock lining and pebbles.

1.Please advise if a cascade at 10m intervals would harm the Koi.

2.What are the precautions for keeping the koi safe from such harsh temperatures.

3. what would be chances of survival of the Koi in higher tempretures.

I interpret “cascades” as “waterfalls” and if so that interval would be just fine- it should inject a good amount of dissolved oxygen into the system and maintain some good flow.

2.

What are the precautions for keeping the koi safe from such harsh temperatures?

40 degrees C is pretty hot and I don’t foresee your koi doing that well in those kinds of temperatures. You really don’t want to exceed 29-30. One thing you can do is install shade (ber that over the pond itself or install shade bearing aquatic plants) and another thing you can do is install chillers. I’ve never had to deal wit chillers but I know that there are companies that make them for that purpose.

My husband and I have noticed a large increase in algae in our pond- maybe about 500 gal- 1000 gal pond. We are at a loss as to what to do to stop this from happening. We have now noticed a serious decrease in the activity of our fish, I haven’t seen them in a few days, haven’t even seen them come up for food. we did have some inclement weather and the temperature around here has begin to drop. I was hoping that they are “hibernating” but because of the algae I cannot see them so I am not sure… any help or advice you can offer is great.

I just started a new pond this spring 5000+ gallons. It has all the filters and has been tested over and over for nitrates ammonia ph alkalinity and phosphates. All are nil or in range respectively. So in theory perfect water conditions. Although only reached 50 F even though temps were consistently over 90 F. I ran it for a few months before I put fish in it and to get the plants up and ready testing it the whole time. The plants (even the hyacinth) all died before I could even put fish in it got plants from separate reputable clean sources. I have taken the plants out and put them in a green house and they have perked right up. I tried to put 6 fish in following all the right procedures and all 6 died the next day. Not due to any predators. So how can I test for chemicals that are not tested in the pond spectrum? Also it may be in my public water supply. How do I filter my tap from unknown chemicals? Or is there something I am missing?

That’s strange that your pond never got over 50F even though it was hot outside -that to me suggests that it is spring fed (but I guess not if you fill it with a public water supply. This issue is obviously outside the realm of most koi pond issues as it deals with chemistries beyond the usual suspects.

There is no chlorine whatsoever. Sorry forgot to ad that

Okay, then you have obviously have something beyond the scope of what is typically tested in koi ponds. It might be worth contacting someone at the nearest university (environmental chemistry dept.) Or local government group who regularly tests local lakes and streams. They will have the equipment to do so.

I have 3 Koi and 5 goldfish in my pond, we live in Birmingham where its cold my small yellow goldfish seems to be bleeding and two koi keep swimming at the surface all day in circles and the other koi and 2 goldfish and 2 shubunkins are hiding at the bottom and come out some times

if you have algae build up that usually means your water contains the fuel to allow the algae to bloom. In this case that fuel would be Ammonia and nitrites etc. So I would definitely get that tested first but yes, those plants could have brought in something unwanted.

I’ve not heard of that happening too often. What other fish do you have in there? Maybe they are scaring them out? Perhaps otters are getting in there? Any signs of external parasites? That may cause them to jump in order to knock parasites off and are inadvertently ending up on the shore.

Hi, I am quite worried about one of my Koi I have had two Koi for many years now, they are both quite large probably around two pounds. they live in an outdoor above ground level tank along with three goldfish, they have all lived there happily for over ten years with no problems, I have a water filter with an ultra violet light tube fitted which keeps the water reasonably clear in summer and also various plants, I do nothing apart from topping up the tank water in a dry summer, I have tested the water and it has all normal readings, I do nothing more than feed them regularly, however one of the Koi has started to keep it’s tail above the water surface, apart from when it’s feeding which it still does well enough but then when finished it always returns to this position, it’s tail appears to be clean and looks no different from the rest of it’s body with no injury or any other visible problem, night or day the fish adopts this position with it’s tail above the surface, he is not entirely in a horizontal position but stays at a downward angle, my other Koi behaves normally. Could my fish be getting old and simply feels better in this position or can anyone identify this behavior with a disease or some other malady? I would be very grateful for any advice.
Brian

My guess would be a swim bladder issue. There is most likely pressure on the swim bladder from a food compaction impeding the normal operation of the swim bladder for regulating proper position in the water column. I would thaw some peas and feed them to the fish -this should penetrate the compaction caused by overeating on your koi’s part.

Hi. I was house sitting my landlords house, and she had a beautiful koi pond that she had for over 40 years… never any problems.
The first day she was gone, everything was fine. I get up the next morning to feed the fish and they are all dead. I am heartbroken and feel so responsible!
We don’t know what could have caused this! Any ideas? Thank you so much!

well, disease usually takes time but one thing that can kill fish pretty quickly is some sort of chemical. A lot of times what happens is that an untrained person adds water to a pond using city water that has enough chlorine to kill the fish. Sometimes its runoff from perhaps an insecticide that was sprayed nearby. Did it rain the night before or was there lighting?

I have 5 koi fish. One of them has become very large and I think it is carrying eggs. My koi at the moment are breeding, but they are ignoring the large one. The males go after the other female in the tank. I’m getting worried that my koi will die from infection from holding her eggs. What do I do?

But you’ll want the egg carrying female to be with the males when she releases eggs or else they won’t get fertilized. Infection won’t be an issue, in the case of fish reproduction any eggs not expelled will get resorbed.
-grant

Hi i’m quite worried about my Koi pond it is 6ft it’s Placed in decking I have very worried about my koi I have lost numerous of fish in the past 3 to 4 weeks I have 2 fish left I have tried cleaning out the filters I have even taken my water to be tested and he is telling me that it could be possible be that they don’t like the weather change or A bacterial infection in the pond NEED HELP BADLY Thanks

I have 10 koi in my pond, all are Ok except one that is 5 years old, it cannot swim straight, its body is curve , thus moving in circles, before that the body is straight and swim straight. Now it swim side ways in circles, the fish stomach is very full.
It feeds with its tail up, looks like it has lost balance and is lethargic . I feed vitamins powder directly thru its mouth, it than has energy to swim, but body is still curve.
What could be the cause and what can I do to solved this problem. Appreciate ur advise.
The Koi is about 22 inches length and could weigh about 2 to 3 kilos.

It could be one of a few things going on. You may have an swim bladder infection (or otherwise not functioning properly) such that the fish cannot inflate/deflate the swim bladder properly. There may be some compacted food in its digestive system and may need only feed to feed the fish some frozen peas. It may also be some kind of internal infection. Try the peas first though.
-Grant

I believe your koi has Epistylis. It’s a parasite and I recommend a salting regime. 2.5 lbs of salt per 100 gals. For two weeks. Divide the total amount that you are going to add and split it into 3 parts and introduce it over 3 days to ease them into it. You can also do potassium permanganate but salt is effective and less harsh. You might as well treat the pond rather than quarantining because the rest will eventually get it. It stems from a water quality issue though so you will need to address that after you clear this up
-grant

We have a koi and about 8 smaller goldfish. My husband mistakenly put bait fish in the pond and they bred. How can I remove the bait fish without hurting the one koi and 8 gold fish? My husband called the bait fish brooder… Could we put a more agressive fish in there that will kill the bait fish? I am lost for solutions!

Please HELP!!! We bought a house in WA one year ago that has a 3,500 pond and there is about 25 big koi fish there. When we bought the house the water was really nice clean but 2 months after the water become so green and we could not see our fish so we hired a professional to come clean our pond but 2 weeks after the water was even worse and for one year we have been doing so many water changes buying so many chemechels and are fish are sick and dying please please help

Anna,
UV is always a good idea for koi ponds as it not only handles free floating algae like what you have but it also kills bacteria and fungus and viruses too. Additionally, Ionizers are also really great assets to have working for your pond as they deal nicely with free floating algae but they are not cheap -you can read about them here. It isn’t necessary to have an ionizer though so for the meantime you can use a product called Accu-Clear. It is a flocculator and essentially grabs and clumps free floating algae then brings it to the bottom where your bottom drain takes it to the filter. Its essential that the clumped algae gets removed from the pond though or the cycle will start anew. It would also help to ramp up your beneficial bacteria colonies with something like Microbe-Lift. Ultimately your water chemistry needs to be at levels that don’t facilitate green water algae in the first place so that needs to be analyzed right off the bat.
Hope this helps.

We bought a house that had a koi pond already. It didn’t have a pump of any kind and it was pure black, but the fish were alive. We hired someone to come out and clean it, replace the liner and re-fill it. The next morning we woke up and the water level was down a bit, but not too much so we didn’t bother with it. That afternoon when we got home from work, half of the water was gone. I called him and he told me to turn the pump off and fill it back up, that it could just be splash out from the pump. So, we did that and the next morning, it was low. Lower than the morning before, but higher than the afternoon so we topped it off and went to work. That afternoon it was low again, so he came out and worked on it. It turns out that the liner had slipped and the pond was leaking. There has been no change in the water level since then(yesterday). Today the fish are dying, we are not able to get in touch with the pond guy this holiday weekend and are worried about out the ones that aren’t dying yet. What can we do?

I have a pond that is 6 ft deep, and about 12 ft across. I have a lot of koi fish but they have been fine. Recently, they have been dying off, all of them have been thoroughly inactive resting mainly at the bottom of the pond, but occasionally the largest are jumping out of the pond. They appear to have a white film on them, but I cannot tell if it is more than what they normally should have. Why are they dying? And how can I help them to not die?

Two things come to mind (and I am inserting sections from my disease article on my site)
1) One of the easiest protozoan parasites to see under a microscope, and subsequently confirm your fish is infected, is Trichodina. An infection of this parasite can be detected by a gray-white opaque appearance on the body of infected Koi. Trichodina is a warm water parasite and can survive in the water for a considerable amount of time without a host. Visually, they are perfectly round with hundreds of little hooks that look like cilia. It rotates continuously as it moves through mucus, causing damage to the Koi’s tissue. This parasite attacks both the skin and gills of your Koi. Infected fish also often show symptoms such as flashing, rubbing and lethargy.
Treating Trichodina: Treat this disease with a five day course of increased salinity (0.5 to 0.6%). Due to increasing tolerance of some organisms to salt treatments a course of formalin may be necessary.
2).
Columnaris: This bacteria will attack sites of injury but will cause fin, tail and mouth rot. Additionally fish can be vulnerable to it during times of stress. Your fish may develop a white film on their skin and display sunken in eyes. It can be a rapid killer so be sure to take swift action.

Ultimately though these things usually have their root in water quality though sometimes pond owners will introduce a new fish in the pond that hasn’t been properly quarantined and disease can be brought in.
-Grant

I had 5 koi, 2 goldfish and 2 oranda goldfish. I Cleaned my pond one day because there was a lot of algae and I could not see anything. I took out all the water and scrubbed the walls of my pond to get all the algae off. I added new water and put the aqua safe liquid in to make sure it was safe for my fish. After one week I had 2 of my koi jump out of my pond and then die within a couple of days later. They did not have anything left of their tail. Then a week later I found another koi dead with its tail also eaten. So today I decided to clean my pond again and found another koi dead! These koi were smaller than the goldfish so I was assuming that the goldfish were attacking the koi? Or is there something I am missing. Also, these goldfish that I got were from my uncle who has a koi/goldfish pond and they reproduced in his pond so he thinks they are half goldfish and half koi. I dont know if that makes a difference but anyways Please help!

Certainly not. Direct UV on a koi or any living creature is bad but with koi pond UV sterilizer systems they are contained and kill only the bacteria, viruses, protozoa and free floating algae that passes by its light. Best of all, there is no chemical residue to worry about.
Here is a link to my filtration article which talks about, in part, UV.
-Grant

Hi have read previous comments and think my fish may have costia, so will be treating again for that, but whenever i clean out the pond filters they have an abundance of red bloodworms, are they a good thing ? as i assume they will eat all the organic matter inc fish poo and un eaten food. Or should i try and get rid of them, i recently built a bigger pond and accidently overstocked it with 12″ to 18″ koi, i have at least double the filters required and about 90w 0f uv an electronic blanket weed killer and 2 air pumps for when the 3ft drop waterfall is off during the night, i have been losing fish regularly since having the new fish, i have treated the pond with salt as well as anti parasite and anti fungus treatments more than once over the last 2 months, am still losing koi, found a dead 18″ koi this morning but was expecting it as it was very lethargic last few days as well could see some scales sticking out on the rear 1/4 of the body and would not move at all, apart from it being dead, could not see anything obvious apart from a reddening of the skin. the rest of the fish appear to look healthy. ive lost 12 so far from young 3″ koi to this 18″ koi, have not lost any goldfish or grass carp, just koi. All the koi have been lethargic before death apart from one 12″ koi which was a complete surprise as it looked normal and healthy. PS pond is under a pine tree and has a sun sail over it to keep sun and pine needles out. running 1x 10k and 1x 5k pump bottom drain fed multi chamber filter with vortex 1x 12k and 1x 8k pressure filters and just about to add a 20k gravity filter.

This is from my site on costia:
Malachite green and 37% formalin can be used but you will need to make sure there is no salt in the pond to start with. If this treatment is chosen be sure to increase aeration.
Not sure if you have tried the above but it might be worth it.
The bloodworms are most likely midge fly larvae-don’t worry about those.
What kind of numbers are you seeing when you test the pond for ammonia, nitrites, nitrates etc? It seems to me like something is off and allowing your pond to become afflicted by something doing a number on your koi (probably costia though if you saw one of your fish with scales raised up that sounds like dropsy).